1. Field of the Invention
The present invention relates to a tuner module that downconverts a received RF (radio frequency) signal into a low frequency intermediate signal.
2. Description of the Related Art
FIG. 1 is a diagram illustrating the structure of a typical tuner module 100 of the related art. The tuner module 100 receives, for example, terrestrial television broadcasting. The tuner module 100 of the related art has a circuit 101 including an air-core coil adjusted manually and an external RF amplifier, and a circuit 102 including an external resonator for a VCO (voltage controlled oscillator). The tuner module 100 of the related art further has a circuit 103 including an external crystal reference signal source and a circuit 104 including a SAW (surface acoustic wave) filter for intermediate frequency (IF) signals (referred to below as intermediate signals). The tuner module 100 of the related art includes about 300 parts and has a large structure, which is, for example, 100 mm wide, 50 mm long, and 14 mm thick.
FIG. 2 is a block diagram illustrating the internal structure of the tuner module 100 of the related art. An RF signal received at an antenna 501A is input to a tuning circuit 502 through an input terminal 501. In response to channel selection by the user, the tuning circuit 502 reduces the signal level outside the frequency band of a desired channel in the RF signal and sets the channel (referred to below as the selected channel) for which the frequency is selected. The RF signal of the selected channel set by the tuning circuit 502 is amplified by a high frequency amplification circuit 503. A mixing circuit 504 mixes the signal supplied by the high frequency amplification circuit 503 and a local oscillation signal oscillated by a local oscillation circuit 505 for frequency conversion and outputs an intermediate signal.
The video intermediate frequency in the tuner module of a typical analog television set of the related art is 58.75 MHz and the image frequency is 117.5 MHz higher than the frequency of a desired signal. Accordingly, the image signal can be attenuated sufficiently by a filter of passive elements included in the tuning circuit 502.
Recently, an ultra-thin television set or the like has come into wide spread use and a tuner module, which is one of the most important components in the television set, is requested to reduce its size and thickness. Many television sets currently incorporate a plurality of tuner modules to support many functions such as recording functions and multi-screen display, and therefore a small-sized tuner module is further requested.
Accordingly, a tuner module that includes a silicon IC (integrated circuit) in which RF circuits are integrated on a semiconductor such as Si or SiGe has been recently adopted in place of the tuner module of the related art, which has many components. The tuner module including a silicon IC in which analog components of the tuner module of the related art are integrated has much less components than the tuner module of the related art, thereby being small-sized. For example, a silicon tuner module 110 in FIG. 3 has a silicon IC in which RF circuits of CMOS (complementary metal oxide semiconductor) transistors are integrated on a semiconductor. Accordingly, the silicon tuner module 110 includes 75 or less components and has a circuit configuration much smaller than the tuner module 100 (see, for example, Japanese Unexamined Patent Application (Translation of PCT Application) No. 2008-521359).